1. Technical Field
The present invention relates generally to a visual display device or method. More particularly, the present invention relates to a personal display device or method that projects an image onto the retina.
2. Description of the Related Art
Visual display devices which present scene and/or data information are not new and have been readily available to the general public since the invention of the television in the mid-twentieth century. Display devices are available for a broad spectrum of applications, from big screen televisions projecting entertainment media, to computer screens projecting information and display generated by a personal computer, to display devices providing positional and systems data to aircraft pilots. Today, visual displays are often the most vital link between man and machine. Personal displays are display devices designed to be viewed by a single viewer, such as Heads-Up Displays (HUDs) in aircraft applications. Such personal displays have only begun to reach maturity, and general availability and usage by a relatively small segment of the general public, within recent years.
FIG. 1 shows a typical display operations sequence of the more common types of display technology, including televisions and computer monitors. A beam source 102, typically electron guns, small accelerators, or similar devices, generates a charged particle beam 109. The charged particle beam is directed into a beam deflection and control system 104. The result is an incident beam 110 which is directed toward an optic screen 106. The incident beam 110 causes the optic screen 106 to direct an image beam 112 into the viewer's eye 108, ultimately projecting an image 114 onto the viewer's retina 116.
FIGS. 2a and 2b show further detail of an optic screen 201 in a typical prior art embodiment. FIG. 2 illustrates a perspective view if a cross-section of the optic screen 201. FIG. 2a is an enlarged cross-sectional view of the cut away edge of the optic screen 201. As described previously, the incident beam 210 is shown directed toward the optic screen 201. Since the 1940s, the incident beam 210 has usually comprised charged particles 212, such as electrons or ions accelerated by a voltage 208. The optic screen 201 is comprised of a first layer 202 which contains a visible light emitting material, a second layer 206 which contains optical material such as phosphors, and a third layer 204 of visible light transparent material. The first layer 202 is transparent to the charged particles 212. Therefore, the charged particles 212 pass through layer 202 and into the second layer 206. There, the charged particle 212 causes an event 216 in which the optical material 214 contained in the second layer 206 emits visible light 218. The first layer 202 is opaque to visible light 218, but the third layer 204 is transparent to visible light 218. Therefore, visible light 218 either travels directly through the third layer 204 or is first reflected from the first layer 202, and then travels through the third layer 204. Upon leaving the optic screen 201, visible light 218 becomes part of the image beam 112 shown in FIG. 1.
The process of fabricating typical display systems with the technologies and/or excitation (incident charged beams) as illustrated in FIGS. 1, 2a and 2b is well known and developed. The methods of using charged beams and materials such as phosphors for achieving visible light, light that can be perceived and used by humans, is also a well established and well understood field of science and technology.
Since the introduction of personal displays, a major effort has been made in industry to reduce the size of visual display devices for applications in a wide variety of fields. As personal display devices become more compact, they become more portable, take up less space when integrated with other display devices, such as in an aircraft cockpit, and weigh less. Some advancements have been made in reducing the size and weight of, for example, portable computer screens, personal television monitors, and numerous other video applications.
Another goal driving the further miniaturization of personal display devices involves attempts to minimize the problem of "total immersion" when a viewer is receiving images from the device. Total immersion is the phenomenon that naturally occurs when a viewer directs his attention to a video output. For example, although there are presently available television monitors in very small formats, such as two inch diameter screens, a viewer must focus his full attention on this small screen in order to have the images projected through his eyes and on to his retina. The viewer, therefore, becomes totally immersed in the task of obtaining information from this personal display device. By way of example, it would be rather hazardous for a viewer to attempt to obtain continuous information from the example television screen while also operating a motor vehicle in traffic. However, if the personal display device could be sufficiently miniaturized so that a small visual beam is directed onto the viewer's retina with a minimally distractive profile of the device itself, the viewer could monitor this information more passively while retaining the ability to see the real world and function accordingly. Such a device would allow a viewer to take in information from both a virtual reality image projected onto his retina and real world images while quickly transitioning between the two images or simultaneously extracting information from both.
The beneficial applications of a personal display device miniaturized to the extent that it is highly portable, interferes minimally with normal vision, and limits the phenomena of total immersion are quite extensive. Miniaturization of display information for an aircraft pilot would allow the pilot to monitor such information without substantially degrading the pilot's ability to monitor other items in the cockpit or conduct visual scans outside the aircraft. A discreet and constantly available monitor for portable personal computers would free up workers to perform manual tasks while obtaining information from the computer. Entertainment applications might include video games mixing virtual reality images with real viewer action. A security officer could monitor video from surveillance cameras while also conducting a visual inspection of other areas assigned to his care. Rather than using overhead projectors or other video equipment, a lecturer could be viewed directly while supporting visual images (teaching aids) are beamed discretely onto the retina of the viewer. A surgeon could monitor the output of miniature optics while simultaneously focusing his attention on other areas on the patient. Despite the numerous potential applications for such miniaturized personal display devices, however, industry has yet to produce such a device that is sufficiently small and inexpensive to manufacture as to be available to the general public in a variety of applications.
Attempts have been made to easily implement a relatively small device capable of operating at the user's discretion in full video type operation, in monitor type operation, in full color, or in monochrome. Such attempts have not been successful as no relatively small device capable of operating at the user's discretion in full video type operation, in monitor type operation, in full color, or in monochrome is currently available. This cannot as yet be achieved with liquid crystal display (LCD) technology or electro-luminescent display (ELD) technology; and plasma display (PD) and cathode ray tubes (CRT) technologies cannot be made small enough. Other potential technologies that have offered more promise by theoretically providing adequate brightness with low power requirements are the use of lasers and light emitting diodes (LEDs). With LEDs, there are more than three decades-old questions of whether or not enough power can be achieved and whether or not the spread of the optical beams can be made small enough to use it in miniaturized applications. So far, there has been very little success or progress with either of these issues so that most, if not all, efforts of any interest have centered around the use of laser emission structures.
There have been several approaches to using lasers and laser diodes for small display applications in the past, but none of them have been successful in producing a miniature personal display device capable of mass production. One of the more frequently suggested and explored concepts is to use laser diodes or LEDs that are singular in color in operation, but mounted or packaged in a two dimensional array. This approach, however, presents multiple problems. Laser diodes and LEDs are single colored or very nearly monochromatic in output because of the materials used to fabricate them. Thus, red devices are of one material/composition, green devices are of another, and blue are yet of another. Putting single devices together in a two dimensional array is called "tiling" and sometimes referred to as mosaic processing. Tiling necessarily adds to the dimensions and complexity of the device. A typical display would have a resolution of at least 640.times.480 elements (m.times.n), which means that more than 300,000 elements would have to be "tiled" together for monochrome operation or 900,000 for full color operation.
Another approach to solving the display problem using laser technology is to use one to three single color lasers in the format of a display device scheme as similarly illustrated in FIG. 1. In this case, a single laser beam with a single color (red, blue, or green) is scanned and focused onto the retina of the eye. If full color operation is desired and/or required, then three lasers would have to be used which then greatly impacts all other parameters of the system in terms of both complexity and mechanical capability. This type of approach has been referred to as the Virtual Retinal Display (VRD), but as yet has not met commercial success. Therefore, a need exists for a relatively small personal display device capable of operating at the user's discretion in full video type operation, in monitor type operation, in full color, or in monochrome. This device needs to require little power to operate, be functional in a variety of diverse applications, and be capable of mass production.
Attempts have also been made to prolong the useful life of light emitting materials used in display systems. Among the deleterious or destructive effects observed with the use of charged particles, such as electrons or ions in bombarding light emitting materials, is a process generally referred to as "aging." This process results in a visibly noticeable reduction in the operational lifetimes of the light materials via decreases in brightness outputs and visual clarity. A need also exists for a display system that suffers less from aging. Any miniaturized personal display that would also reduce aging problems would be of further commercial benefit.